An image sensor comprises a plurality of pixels, each pixel including: a light-receiving element that outputs an output voltage that varies in response to a photon entering; at least one comparator that compares the output voltage with a plurality of mutually-different threshold voltages and outputs a single signal each time the output voltage varies so as to exceed either of the threshold voltages; and at least one counter that counts a number of signals output by the comparator upon comparing the output voltage with the plurality of threshold voltages and outputs a count value, for each of the threshold voltages.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An image sensor comprising a plurality of pixels, each pixel including: an avalanche photodiode that is driven in Geiger mode and outputs an output voltage that varies in response to a photon entering; a quenching resistor; at least one comparator that compares the output voltage with a first threshold voltage or a second threshold voltage different from the first threshold voltage and outputs a single signal each time the output voltage varies so as to exceed either of the first and second threshold voltages; and at least one counter that counts a number of signals output by the comparator upon comparing the output voltage with the first and second threshold voltages and outputs a count value, for each of the first and second threshold voltages.
2. The image sensor according to claim 1 , wherein the comparator includes: a first comparator that compares the output voltage with the first threshold voltage and outputs a single signal each time the output voltage varies so as to exceed the first threshold voltage; and a second comparator that compares the output voltage with the second threshold voltage and outputs a single signal each time the output voltage varies so as to exceed the second threshold voltage, and the counter includes: a first counter that counts a number of signals output from the first comparator and outputs a first count value; and a second counter that counts a number of signals output from the second comparator and outputs a second count value.
3. The image sensor according to claim 2 , wherein a difference between the output voltage and the first threshold voltage when a photon is not entering is lower than a difference between the output voltage and the second threshold voltage when a photon is not entering.
4. The image sensor according to claim 1 , wherein each of the plurality of pixels further includes a switch that switches between the first threshold voltage and the second threshold voltage and supplies the voltage to the comparator; and the counter counts a number of signals output from the comparator when comparing the output voltage with the first threshold voltage and outputs a first count value, and counts a number of signals output from the comparator when comparing the output voltage with the second threshold voltage and outputs a second count value.
5. The image sensor according to claim 4 , wherein a difference between the output voltage and the first threshold voltage when a photon is not entering is lower than a difference between the output voltage and the second threshold voltage when a photon is not entering.
6. The image sensor according to claim 1 , wherein the plurality of pixels are all the pixels in the image sensor.
7. The image sensor according to claim 1 , further comprising: a determinator that determines that a pixel for which a difference between the count values obtained for the first and second threshold voltages is greater than or equal to a predetermined threshold is a saturated pixel.
8. The image sensor according to claim 7 , wherein a predetermined count value is output to the exterior of the image sensor from the pixel determined to be a saturated pixel.
9. An image sensor comprising: a pixel array including a plurality of first pixels and a plurality of second pixels, each pixel having an avalanche photodiode that is driven in Geiger mode and outputs an output voltage that varies in response to a photon entering, wherein each of the first pixels includes: a first quenching resistor; a first generator that generates a first threshold voltage; a first comparator that compares the output voltage with the first threshold voltage and outputs a single signal each time the output voltage varies so as to exceed the first threshold voltage; and a first counter that counts a number of signals output from the first comparator and outputs a first count value, and each of the second pixels includes: a second quenching resistor; a second generator that generates a second threshold voltage different from the first threshold voltage; a second comparator that compares the output voltage with the second threshold voltage and outputs a single signal each time the output voltage varies so as to exceed the second threshold voltage; and a second counter that counts a number of signals output from the second comparator and outputs a second count value.
10. The image sensor according to claim 9 , wherein a difference between the output voltage and the first threshold voltage when a photon is not entering is lower than a difference between the output voltage and the second threshold voltage when a photon is not entering.
11. The image sensor according to claim 9 , further comprising: a determinator that determines that a pixel for which a difference between the count values obtained for the first and second threshold voltages is greater than or equal to a predetermined threshold is a saturated pixel.
12. The image sensor according to claim 11 , wherein a predetermined count value is output to the exterior of the image sensor from the pixel determined to be a saturated pixel.
13. An image capturing apparatus comprising: the image sensor comprising a plurality of pixels, each pixel including: an avalanche photodiode that is driven in Geiger mode and outputs an output voltage that varies in response to a photon entering; a quenching resistor; at least one comparator that compares the output voltage with a first threshold voltage or a second threshold voltage different from the first threshold voltage and outputs a single signal each time the output voltage varies so as to exceed either of the first and second threshold voltages; and at least one counter that counts a number of signals output by the comparator upon comparing the output voltage with the first and second threshold voltages and outputs a count value, for each of the first and second threshold voltages; and a determinator that determines that a pixel for which a difference between the count values obtained for the first and second threshold voltages output from the image sensor is greater than or equal to a predetermined threshold is a saturated pixel.
14. An image capturing apparatus comprising: the image sensor comprising: a pixel array including a plurality of first pixels and a plurality of second pixels, each pixel having an avalanche photodiode that is driven in Geiger mode and outputs an output voltage that varies in response to a photon entering, a first quenching resistor; wherein each of the first pixels includes: a first generator that generates a first threshold voltage; a first comparator that compares the output voltage with the first threshold voltage and outputs a single signal each time the output voltage varies so as to exceed the first threshold voltage; and a first counter that counts a number of signals output from the first comparator and outputs a first count value, and each of the second pixels includes: a second quenching resistor; a second generator that generates a second threshold voltage different from the first threshold voltage; a second comparator that compares the output voltage with the second threshold voltage and outputs a single signal each time the output voltage varies so as to exceed the second threshold voltage; and a second counter that counts a number of signals output from the second comparator and outputs a second count value; and a determinator that determines that a pixel for which a difference between the count values obtained for the respective threshold voltages output from the image sensor is greater than or equal to a predetermined threshold is a saturated pixel.
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July 23, 2019
August 31, 2021
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